I know how to make overlay text pop onto the screen over background video, and to make text fade in over background video.
It would be cool if other transitions could be used to bring in text overlays. Typewriter and zoom effects come to mind as well as conventional wipes and slides.
It would also be cool to make text scroll/crawl horizontally or vertically? Or can Shotcut already do this and I haven’t discovered it yet?
It can. 
Here’s how to make text scroll:
https://www.youtube.com/watch?v=i3FQdBCVZgY
And have you seen @jonray’s great video tutorials on doing text in Shotcut?
https://www.youtube.com/watch?v=Feftwy4PL44
He also made a detailed 4 part series on working with HTML for text. It’s the only video tutorial of its kind about HTML regarding Shotcut that I know about:
https://www.youtube.com/watch?v=AhX5p_umORM
https://www.youtube.com/watch?v=vkBSNAnA3Yw
https://www.youtube.com/watch?v=bUvGVZUhHpE
https://www.youtube.com/watch?v=9x3wdROpKVU
He has even more tutorials on his youtube channel.
There is a lot of stuff available for using the Text: HTML (or as it used to be called Overlay HTML) filter, including titles, typewriter effects, flying text, exploding images, WrbGL transitions, CSS3 animations, etc… See http://www.elusien.co.uk/shotcut/ for examples. Also, search the posts for “HTML”.
Did you try the presets of the text filter? There are various pan and zoom types available.
